Conventionally, there are various cases where a plurality of measurement targets is accurately aligned in positions in order to evaluate both of the measurement result. The plurality of measurement targets are, for example, a measurement point of a reference measurement target and a measurement point of a measurement target.
For example, in color matching of printed materials by offset printing, in the printing industry, when management of color quality of printed materials in offset printing is performed, measuring of colors of a color chart called a control strip is performed when the colors of a final contract proof (final proof) which is proofed with the customer's approval and a printed material printed by a printing press are matched.
In this color measurement, a spectrophotometer (for example, see Patent Literatures 1 and 2) is generally used. Here, the control strip includes, for example, approximately 200 small measurement patches according to the print size which are called color patches and are generally approximately 5 to 6 mm in square and arranged in a line. The control strip is printed in a white blank of a sheet outside a printing surface of a printed material so as to extend long on the entire width (effective printing range) of a printing press.
Moreover, the color patch is arranged so that the solid patches having density of 100% for each ink colors (cyan, magenta, yellow, and black) are repeatedly arranged in each units of ink fountain key to control a print color. These color patches are used for checking whether an image is printed in appropriate density and L*a*b* values or for checking the uniformity of color on the entire surface of a printed material by measuring the respective density values and the L*a*b* values.
However, ink is transferred from an inking roller to a plate cylinder by the physical pressure of the inking roller of the printing press and a chemical action (repulsion of water and oil), and then, is sequentially transferred from a blanket cylinder (a transfer surface made from rubber) to a print sheet (close to an impression cylinder). Thus, practically, the transfer of ink on the entire surface of the print sheet is not always constant. Thus, it is not possible to accurately check the color reproduction in a picture (image) of the printed material using the color patches only.
Thus, various attempts have been made to directly measure the color of a picture (image) in addition to measuring the colors of the color patches. However, there is a problem that it is difficult to realize positioning for measuring the same points of a final proof and a printed material. For example, a spectrophotometer disclosed in Patent Literatures 1 and 2 facilitates positioning of measurement points by capturing the images of the measurement points. However, a technique for aligning the same measurement points of different measuring targets such as the final proof and the printed material has not been developed.
Positioning may be realized using an X and Y position control device. However, in this case, the system may become expensive, and an accuracy error will be occurred by expansion and shrinking of paper due to humidity and the like, or caused by the accuracy of an output recorder. As a result, the size of a final proof and a printed material may be different or a partial dimensional error may occur. Moreover, it is necessary to develop software that can assemble setting conditions corresponding to various individual conditions. This is because page imposition of double-page spread used for print proof and page imposition layout for a book print (pagination) are completely different in page printings. Thus, it is only possible to realize rough positioning with a simple method and it is difficult to obtain stable measurement results. Furthermore, since the measurement value is different depending on the direction of a picture with respect to a measuring instrument, it is difficult to obtain sufficient measurement accuracy with only the X and Y position control device.